1. Field of the Invention
This invention relates to a photographic flash device comprising a constant-voltage source which controls oscillation function of a DC-DC converter and makes a charging voltage of a main discharging capacitor constant. It is more particularly directed to an apparatus having a function of indicating states of the charging voltage value of the main discharging capacitor in the photographic flash device.
2. Prior Art
In the conventional photographic flash device (hereinafter referred to strobe), one typical type of the indication apparatus for the charged voltage value of the main discharging capacitor is so devised that an indication device such as neon tube is connected to the main discharging capacitor in parallel. Indication operation for the charging voltage of the main discharging capacitor is made in accordance with states whether the indication device lights up or not. In such conventional indication apparatus the indication device lights up when the voltage across the main discharging capacitor rises up to a specified value which is usually the minimum voltage necessary for strobe action. But it is not possible to detect to what value the voltage of the main discharging capacitor rises after passing the minimum voltage of the main discharging capacitor. Therefore, there has been an uncontrollable factor in the strobe action. In other words, amount of the flashed light differs depending on the progress of charging of the main discharging capacitor. For example, the charged voltage which is immediately after the lighting of the indication device is considerably lower than that when the main discharging capacitor is fully charged after a lapse of a long time from the lighting. This fact reflects to a problem of undesirable variation of the amount of flashed light, and thus no uniform flashing can be expected.
In order to solve the abovementioned problem, a photographic flash device was proposed and disclosed in the specification of U.S. Pat. No. 3,831,079 to West Electric Co., Ltd. In the photographic flash device of the U.S. Patent, a DC-DC converter is made to intermittently oscillates when the charged voltage of the main discharging capacitor rises up to a specified value, and thus the charging voltage of the main discharging capacitor is held at a constant value. Simultaneously, a light emitting display device such as electroluminescence and light emitting diode, which is connected to the DC-DC converter, begins blinking. In such device, when the flash tube is lighted up during the blinking operation of the light emitting display device, amount of the flashed light is always constant since the charged voltage across the main discharging capacitor is held at the constant value. Therefore, by making a flash during the period of the blinking, the photographic flash device can be free from the problem in the variation of the flashed light amount. But when strobe action is urgently required and hence is made when the charging voltage does not yet reach the final constant value though higher than the minimum voltage for flashing, the amount of the flashed light is an uncertain one which is lower than the constant value. Therefore, the amount of the flashed light is beyond control. This is due to the fact that the voltage indication by the conventional light emitting display device can indicate only one state that the voltage of the capacitor is above a preset value.